Manufacture of gelatin



PatentedFeb.20, 1940 p I 2913M TTNITED STATES PATENT oFFlcE o SamuelE., Sheppard and James H. Hudson,.Roch-'- ester, N, Y., assigncrs to Eastman Kodak Company, Rochester, N. Y., a corporationof New Jersey No Drawing. Application July15, 1938,

Serial No. 219,429

Claims. (Cl. 260-418) This invention relates to a process of productrio field. Thisfcon'dition results from the neuing gelatin for photographic uses. T tralization of the positive and negative ions in T The gelatin used in photographic emulsions or solution. In our prior Patent No. 2,101,877, we other photographic layers is subjected, during ref-erredto the colloidal properties of gelatim M the processing of the films or plates on which such as-swellingin water, change in viscosity in' theTlayers are coated, to alternate alkaline and aqueous solution and precipitation from solution acid baths. The gelatin must, therefore, withby alcohol and grouping these properties together stand changes from high to a low pH and vice as general physical properties of the gelatin. It versa and, if this change in pH passesthrough is known that, in general, these various physical theiso-elctric point of the gelatin, there is-an properties are at a minimum value at the same alternate swellingand contraction of thegelatin pH and this minimum of physical values has been which tends to lower the quality of the phototaken asanindex of the iso-electric point'of the graphic image. gelatin. T w In our prior Patent No. 2,101,877, granted De- The iso=electric point of gelatin depends upon cember 14, 1937, we described a process of prethe conditions under which it is extracted from paring photographic gelatin having an iso-electhe hidesr- Gelatin extracted in the usual way by trio point at a higher range on the pI-I scale, so a lime treatment of hides has an iso-electric point that the minimum region of colloidal properties, ata pH of about 4.7 to 5.1. The gelatin prosuch as swelling in water and change in viscosity duced by the acid process of our prior Patent No.

in alkaline solution, was higher on the pH scale 2,101,877 has an iso-el-ectric point in the region-of 20 than-in the case of the ordinary gelatin obtained pH 7" and upward,- and the properties are not, by lime treatment of hides. Our prior process nearlyso sharply defined at one point as in the consisted-in carrying out the entire hide treat case of theelime-processed gelatin. This means ment processes of dehairing and plumping, in an that the physical properties, such as swelling,

acidsolution. T change more gradually with change in pH in the 25 Our investigations have shownthat the de caseof theacid-type gelatin. hairing of hides for the purpose of producing In the customary alkaline treatment of hides gelatin from them is most readily and speedily preparatory to extraction of gelatin, the hairs effected in alkaline baths, particularly at a pH are dislodgedand there is a swelling or penetraof 10 or higher. T T tion of the surface or epidermal layer by the al- 30 It is, therefore, an object of the present inkaline bath. The penetration continues into the vention to providea methodfor obtaining a phohides and it is this treatment which results in. tographic gelatin from animal hides in as conthe gelatin of low iso electric point. In the acid venient and rapid a manner as possible, while at treatment described-incur Patent No. ,101,877,.

the same time producing gelatin havingan isothere is little swelling of the hide surface. In 35 electric pointin the region of pH 6 to 7 or higher. this case, the individual hairs do not detach A 'furtherTobject is to provide a more rapid rneththemselves from the skinbut the whole epidermal od for obtaining gelatinfrom hides. A still furlayer fi y l p Carrying the ai l ll it. This then object isto provide method for preventing action is liable to be somewhat'unequal especially 10 swelling. of the hide material during the dehairwith the skins of older animals and, for this rea 40 ingtreatment; Other objects will appear from son, the treatment is not always satisfactory. the following description of our invention. This'condition can be avoided, however, by re- These objects are, accomplished according to stricti on of the swelling action of an alkaline our invention and a gelatin of high iso-electric bath-designed to dehair the skin, to the surface region is produced by carrying out the dehairing or epidermal layer whereby the action of the al- 45 operation in an alkaline medium, but with a T kaline rn aterial'is limited to a chemical reduction sufficient concentration of neutral salt present of the keratin of the hair roots, so that thehair to prevent plumping or swelling of the hide maslips out easily onslight rubbing. This chemical terialby the alkaline bath. The subsequent opaction isprobably the conversionof disulfide link- T oration ct plumping is then carried out in acid again the keratin to twoS H groups. This type 50 medium, as described in our prior Patent No. of dehairingwhich corresponds tothat effected 2,101,877. in regular lime baths, except in that plumping of Theiso electricpoint of a gelatin has been, the hide is prevented is, therefore, entirely difdefiried as the condition at which there is no mi ferent' fromthat which occurs in a wholly acid gration-to the anode or thecathode in an electreatment of the hides. If the alkaline treatment 55 is carried out in the usual way, it does result in swelling of the hide substance but, by providing a sufficient concentration of neutral salt in the alkaline bath, the plumping or swelling of the hide material is prevented, while, at the same time, allowing the chemical reduction to proceed so that the hairs may be readily removed.

' tion containing 1% NaOH and 7% Na zSO3. Af-

After the dehairing treatment which requires from several days to a week, the hairs may be removed by slight rubbing, such as by washing in a mill. The stock is then removed to-an acid plumping bath where it is left for a 'sufiicient length of time for full plumping or swelling to .hide selected at random and treating thefresh' surfaces in turn with the followingindicators to determine the pH:

pH Bromocresol Green 4.0-5.6 Chlorphenol Red 5.2-6.8 Bromthymol Blue 6.0-7.6

This illustrates the pH range which may be indicated by various compounds. Color nuance may be estimated by these dyes with an-accuracy pH of .2 to .4.

When the central portions of the hide have attained the pH desired, the material is subje'cted to extraction with hot water at a tem perature'of 160 to 180 F. The pH at which extraction takes place may vary and, although it may be as high as 6 or 7, we have found that a pH of 5 is satisfactory because this is not so acid as to produce excessive hydrolysis of the gelatin while, on the other hand, it is sufiicient 1 acid to prevent saponiflcation of fats and, therefore, to allow their ready separation, The gelatin liquor is then filtered and may be vacuum concentrated before chilling and drying.

The following examples which are illustrative only indicate several methods of extracting gelatin, according to the present invention.

Example I A quantity of green calf hide was washed to remove excess salt, dirt and other foreign mat' ter and was then treated with an aqueous soluter twenty-four to seventy-two hours, the hair was found to slip easily from the hide and was removed by washing the stock in a mill. It was then removed by washing the stock in a mill. It was then removed to an acid plumping bath composed of a 1% solution of hydrochloric acid in water. After remaining in the plumping bath forl l days, the hides were removed and neutralized to a pH of about 5. The gelatin was then extracted from the hides by treating them with hot water at a temperature of 170 F. and the gelatin liquor removed by filtration. The gelatin obtained in this way had a pH of about 5, and an isoelectric point at pH 7 to 9.

Example II p A quantity of hide stock was Washedto remove foreign matter and w s then treated in an about 6.

. hides were treated for about fifteen days.

aqueous solution containing 1% NaOH and 1% Nazsos. After three days, the hair was removed by washing and the hide was then transferred to a plumping bath consisting of an 0.8% hydrochloric acid solution in water. The hides were allowed to remain in the plumping bath for twenty-one days and, after neutralization, the gelatin was extracted in the usual way and was found to have an isoelectric point at pH of Example III A quantity of hides was washed to remove foreign matter and was then subjected to a dehairing bath containing 0.66% NaOI-I and 6.6% NazSOs in water. After six days, the hair was removed by washing and the hides were transferred to a plumping bath. This bath consisted of a 1% acetic acid solution in water and the They were then. removed from the bath and neutralized and the gelatin extracted in hot water in the usual way to produce agelatin having an isoelectric point at a pH of about 6.8.

Example IV although calcium hydroxide and sodium hydrox ide are found to be most suitable. The strength of alkali may vary from 4% to about 1% or higher.

This bath may contain any neutral inorganic salt, such as sodium sulfite, sodium sulfate,

sodium acetate, calcium sulfate, calcium chloride, calcium nitrate, calcium acetate, sodium chloride, sodium nitrate, potassium sulfite, potassium sulfate, potassium chloride, potassium nitrate, and others. The concentration of the neutral salt must be such that swelling of the hide material is prevented, a concentration of from about 1% to about 10% or more of the neutral salt having been found to be satisfactory. The hides may be treated in the dehairing bath for periods varying from about twenty-four hours to about a week.

The plumping treatment of the hides may be carried out as described in our prior Patent No. 210L877 in a dilute solution of a weaklyionized acid, for example, a to 10% solution of acetic or propionic acid, or in a dilute solution of a. strongly ionized acid, such as hydrochloric or sulfuric of a strength of about 0.1% to about 1.0%. The length of plumping treatment may be varied, depending upon the strength of the acid used and the desired pH of the resulting gelatin. Usually a period of from two days to twenty-five alkaline solution containing from 1% to 10% of a 5 tofl, and extracting the gelatin fromthem in neutral salt to prevent swelling of the hide material, removing the hides from the dehairing 1 bath and subjectingithem to plumping in an acid bath, neutralizing the hides to a pH of about 5v to '7, and extracting the gelatin from them in Water solution. t

2. The method of preparing photographic gelatin having an iso electric point in the region pH6 to pI-IQ, which comprises subjecting animal hides "bath, neutralizing the hides to a pH of about .to a dehairing treatment in a A, to 1% calcium hydroxide solution containing from 1% to 10% of a neutral salt to prevent swelling of the hide material, removing the hides from the dehairing bath and subjecting them to plumping in an acid bath, neutralizing the hides to a pH .of about ,from them in water solution.

Water solution.

4. The method of preparing photographic gela tin having an iso--electric point in the regionpI-IG to pit-I9, which comprises subjecting animal hides toa dehairing treatment in a A; to. 1% sodium hydroxide solution containing from 1% to 10% of a sodium salt of an inorganic acid to prevent swelling of the hiole material, removing the hides from the dehairing oath and. subje'ctingthem to plumping in an acid bath, neutralizing the hides to a pH of about 5 to 'Land extracting the gelatin from them in water solution. i 1

5 The method of preparing photographic gelw tin having an iso-electric point in the region pH6 top'HS, which comprises subjecting animal hides to a dehairing treatment in a to 1% calcium hydroxide solution containing from 1% to 10%1 of a sodium salt of an inorganic acidto prevent swelling of the hide material, removing the hides from the dehairing bath and subjecting them to plumping in an acid bath, neutralizing the hides to a pH of about 5 to 7, and extracting the gelatin SAMUEL E. SHEPPARD.

JAMES H. HUDSON. 

